1. Field of the Invention
The present invention relates to a projection display apparatus, and more particularly, to a projection display apparatus capable of simplifying a structure of an optical system and reducing costs by using a polarization beam splitter having two splitting surfaces.
2. Discussion of the Related Art
As displays are large-sized, development of data projector, projection TV, projection monitor and the like, which use projection techniques, is being accelerated. In addition, recently, reflective liquid crystal panels have been applied to projection-type liquid crystal projectors. The reflective liquid crystal panels are display panels which can improve an aspect ratio by forming reflective electrodes on pixels. Since these reflective liquid crystal panels can increase the aspect ratio much more than the conventional transmissive liquid crystal panels, it is possible to implement projectors which are downsized and have high efficiency.
In general, projectors can be divided into a lighting system, a color separation/synthesis system and a projection system. In the projectors, if the reflective LCD is used as an imager, polarized light should be irradiated into the imager so as to change a traveling path between the lighting system and the projection system.
FIG. 1 is a view of a conventional three-plate transmissive projector. Referring to FIG. 1, the conventional three-plate transmissive projector includes: a light source 110 for applying non-polarized lights; a polarizer 120 for polarizing the non-polarized lights in one direction to generate polarized lights; a first dichroic mirror 130 for reflecting red light among the polarized lights and transmitting green and blue lights among the polarized lights; a first mirror 140 for totally reflecting the red light reflected by the first dichroic mirror 130; a second dichroic mirror 150 for reflecting/transmitting the green/blue lights transmitted by the first dichroic mirror 130, respectively; second and third mirrors 160a and 160b for totally reflecting successively the blue light transmitted by the second dichroic mirror 150; first, second and third LCD panels 170a, 170b and 170c for selectively transmitting the red light totally reflected by the first mirror 140, the green light reflected by the second dichroic mirror 150 and the blue light reflected totally by the third mirror 160b; and a synthesis prism 180 for synthesizing the red/green/blue lights selectively transmitted by respective panels and outputting the synthesized light.
In the transmissive projector, the polarized light of red light(R), green light (G) and blue light passing through the polarizer 120 from the light source 110 is selectively transmitted or reflected. In other words, the first and second dichroic mirrors 130 and 150 reflect the red light and the green light sequentially, and transmit the remaining blue color. Then, the LCD panels 170a, 170b and 170c selectively transmit the reflected red/green/blue lights. Afterwards, the synthesis prism 180 synthesizes the transmitted red/green/blue lights to thereby obtain desired images.
FIG. 2 is a view showing a conventional three-plate reflective projector. Referring to the FIG. 2, the conventional three-plate reflective projector includes: a light source 210 for applying non-polarized lights; a polarizer 220 for polarizing the non-polarized lights in one direction to generate polarized lights; a first dichroic mirror 230 for reflecting red and green lights among the polarized lights and transmitting blue light among the polarized lights; a second dichroic mirror 250 for reflecting/transmitting the green/red lights reflected by the first dichroic mirror 230, respectively; a mirror 240 for totally reflecting the blue light transmitted by the first dichroic mirror 230; first, second and third polarization beam splitters 260a, 260b and 260c for changing a traveling path of light by reflecting or transmitting the red and green lights separated by the second dichroic mirror 250 and the blue light totally reflected by the mirror 240; first, second and third LCD panels 270a, 270b and 270c for selectively deflecting the red/green/blue lights, which are reflected by the first to third polarization beam splitters, by 90xc2x0 according to image signals; and a synthesis prism 280 for synthesizing the red/green/blue lights reflected by the respective panels.
According to the conventional projectors constructed as above, a large number of dichroic mirrors, mirrors and polarization beam splitters are used so as to split non-polarized light into the red/green/blue lights and guide them to the respective LCD panels.
In that case, the optical system is complicated and increases in volume, so that it is difficult to downsize the optical system.
In particular, high precision is required since the dichroic mirror and the polarization beam splitter, which are used to construct the conventional projector, influence an entire performance of the projector according to their qualities. Accordingly, there is a limitation when using these optical components since they are expensive.
An object of the present invention is to provide a projecting display, capable of saving optical components by using a polarization beam splitter having two splitting surfaces and reducing a unit cost of an optical system.
Another object of the present invention is to provide a projection display apparatus capable of making it easier to design lens using improved polarization beam splitter.
To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a polarization beam splitter comprises: a first splitting surface for transmitting green and blue lights regardless of a P polarized light or an S polarized light, transmitting a red light if the red light is the P polarized light, and reflecting the red light if the red light is the S polarized light; and a second splitting surface for transmitting the green and blue lights if the green and blue lights are the P polarized lights, reflecting the green and blue lights if the green and blue lights are the S polarized lights, and transmitting the red light regardless of the P polarized light or the S polarized light. The first splitting surface is formed in a diagonal direction from one side of a first incident surface upon which the red light is incident. The second splitting surface is formed in a diagonal direction from one side of a second incident surface upon which the green and blue lights are incident.
In accordance with another preferred embodiment of the present invention, a polarization beam splitter comprises: a first splitting surface for transmitting green and blue lights regardless of a P polarized light or an S polarized light, transmitting a red light if the red light is the P polarized light, and reflecting the red light if the red light is the S polarized light; and a second splitting surface for reflecting the green and blue lights if the green and blue lights are the P polarized light, transmitting the green and blue lights if the green and blue lights are the S polarized light, and transmitting the red light regardless of the P polarized light or the S polarized light.
In accordance with further another preferred embodiment of the present invention, a projection display apparatus comprises: a light source for applying a non-polarized light; a polarizer for polarizing the non-polarized light in one direction to generate polarized lights; a dichroic mirror for reflecting a red light among the polarized lights and transmitting green and blue lights among the polarized lights; a mirror for changing a traveling path of the red light reflected by the dichroic mirror; a polarization state converter for selectively converting polarization states of the green and blue lights transmitted by the dichroic mirror; an LCD panel for displaying images corresponding to the red/green/blue lights; a polarization beam splitter for selectively transmitting or reflecting the lights according to the polarization states of lights provided from the mirror and the polarization state converter, and synthesizing lights containing the images provided from the LCD panel; and a projection lens for magnifying and projecting the synthesized images outputted from the polarization beam splitter on screen.
The polarization state converter converts the green light into the S polarized light and the blue light into the P polarized light.
If an image signal is inputted, the LCD panel is a reflective panel that changes the phases of the respective lights by 90xc2x0 and reflects the changed lights.